1. Field of the Invention
The present invention relates generally to aperture correction circuits in which an aperture correction signal formed from an input video signal is added to the input video signal and then generated as an output signal. More particularly, this invention relates to an aperture correction circuit for use with video apparatus such as a video camera or the like.
2. Description of the Prior Art
In a video apparatus such as a video camera and the like, a transversal filter, a band-pass filter or the like is employed to form an aperture correction signal from an input video signal so as to emphasize the outline of a picture. Then, this aperture correction signal is added to the input video signal to increase the resolution of a picture.
In the prior art, various signal processings such as an aperture correction and the like for a video signal are carried out in the form of an analog video signal in an analog signal processing system or in the form of a digitized video signal in a digital signal processing system.
In the conventional aperture correction circuit, an aperture correction signal linearly proportional to the signal level of the input video signal is generated by the transversal filter, band-pass filter or the like, and the aperture correction is performed by the analog signal processing system or the digital signal processing system that effect the linear operation. As a result, the
amount of correction is small at the portion of the picture having low contrast so that the aperture correction effect, such as the emphasized sharpness of the picture and the improved apparent contrast of the picture, cannot be achieved satisfactorily. Further, the aperture correction amount is too large at the portion of the picture having high contrast so that the picture looks unnatural. Particularly, when the video signal is digitized and the aperture correction processing is performed by the digital signal processing system, the amount of the aperture correction is noticeably insufficient at the portion of the picture having low contrast or the amount of the aperture correction is remarkably large at the portion of the picture having high contrast.